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Re: xfs i_lock vs mmap_sem lockdep trace.

To: Dave Jones <davej@xxxxxxxxxx>, Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Subject: Re: xfs i_lock vs mmap_sem lockdep trace.
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 31 Mar 2014 10:43:35 +1100
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140329223109.GA24098@xxxxxxxxxx>
References: <20140329223109.GA24098@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Sat, Mar 29, 2014 at 06:31:09PM -0400, Dave Jones wrote:
> Not sure if I've reported this already (it looks familiar, though I've not 
> managed
> to find it in my sent mail folder).  This is rc8 + a diff to fix the stack 
> usage reports
> I was seeing (diff at http://paste.fedoraproject.org/89854/13210913/raw)
>  ======================================================
>  [ INFO: possible circular locking dependency detected ]
>  3.14.0-rc8+ #153 Not tainted
>  -------------------------------------------------------
>  git/32710 is trying to acquire lock:
>   (&(&ip->i_lock)->mr_lock){++++.+}, at: [<ffffffffc03bd782>] 
> xfs_ilock+0x122/0x250 [xfs]
> but task is already holding lock:
>   (&mm->mmap_sem){++++++}, at: [<ffffffffae7b816a>] 
> __do_page_fault+0x14a/0x610
> which lock already depends on the new lock.

filldir on a directory inode vs page fault on regular file. Known
issue, definitely a false positive. We have to change locking
algorithms to avoid such deficiencies of lockdep (a case of "lockdep
considered harmful", perhaps?) so it's not something I'm about to


Dave Chinner

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